1. Field of the Invention
The present invention relates to a polishing composition, a process for producing a substrate comprising applying the polishing composition and a process for preventing clogging of a polishing pad.
2. Discussion of the Related Art
Hard disks have been greatly developed over the years in the trends of miniaturization and high capacity, so that the trend of high density has been progressed. Consequently, the minimum recording area has become smaller, and the floating amount of a magnetic head has been made increasingly smaller. Therefore, there have been desired to reduce the surface roughness and the fine waviness, and to reduce surface defects such as scratches and pits in a hard disk substrate. With this trend of development, a harder polishing pad having a smaller pore size has been used in a step of polishing the substrate. Also, for the same reasons, the average particle size of the abrasive has become smaller. However, in these polishing pads, abrasive grain debris and polishing debris are retained and likely to be adhered to the pad pores, so that clogging is likely to take place during continuous polishing. Consequently, the polishing rate is lowered and surface defects such as pits are generated in the polished substrate, so that frequent dressing of the polishing pad is necessitated, thereby lowering the workability of polishing and lowering productivity of the polished substrate. Therefore, there has been desired a polishing composition which reduces clogging to the pad pores. As polishing compositions in which the polishing pad is less likely to be clogged, a composition comprising a molybdate and a specified organic acid is disclosed in Japanese Patent Laid-Open No. Hei 7-216345; and a polishing composition comprising water, an alumina abrasive and a molybdate is disclosed in Japanese Patent Laid-Open No. Hei 5-311153. However, any of these composition do not satisfactorily meet the requirements of the reduction in surface defects and the reduction in clogging.
An object of the present invention is to provide a polishing composition in which clogging of a polishing pad is reduced, a process for producing a substrate comprising polishing a substrate to be polished using the polishing composition, and a process for preventing clogging of a polishing pad.
Another object of the present invention is to provide a polishing composition by which there are eliminated the problems in the lowering of the polishing rate when subjected to continuous polishing due to generation of clogging, and in the prevention of the generation of surface defects such as pits, whereby lowering the frequency of the dressing, and thereby improving the workability and the productivity; a process for producing a substrate comprising polishing a substrate to be polished with the polishing composition; and a process for preventing clogging of a polishing pad comprising applying the above-mentioned polishing composition.
These and other objects of the present invention will be apparent from the following description.